This invention relates to semiconductor pressure sensors, and to improved methods for manufacturing such devices.
Semiconductor pressure sensors and strain gages are commonplace today. Their extremely small size, less than 0.125 inch in any dimension, is typical. High durability to outside forces makes these devices popular for the pressure measurement needs of hydraulic and aerodynamics forces, among other applications.
Typically, semiconductor pressure sensors contain a diaphragm of one or more silicon layers for deflecting in response to opposing pressure environments, and piezoresistive elements that are configured for sensing the direction and/or magnitude of diaphragm deflection.
The manufacture of these sensors makes the diverse range of devices available today and one aspect of the invention provides improvements in that manufacture. Because high temperature stability is often required, improvements relating to sensor heat stability is an active research area. Dielectric isolation is one technique which increases stability. The dielectric ideally isolates semiconductor piezoresistive elements from the diaphragm, the support structure, and other piezoresistive elements. Silicon dioxide, SiO.sub.2, exemplifies a known dielectric that maintains a nearly constant resistance over significant temperature changes.
The type of silicon used in the pressure sensor is also important. Single-crystal silicon and polycrystalline silicon materials have different properties that influence mechanical strength, sensitivity, and even manufacturability.
Despite the advances made in semiconductor physics, pressure sensors with improved temperature stability and higher pressure sensitivity are sought, particularly for use in hostile environments Devices available today generally have limited sensitivity and dielectric isolation, that restrict stability and high temperature operation.
In U.S. Pat. No. 4,672,354 for "Fabrication of Dielectrically Isolated Fine Line Semiconductor Transducers and Apparatus", for example, glass is used as an insulator and as a bonding agent. Such a pressure transducer is difficult to manufacture, and has other undesirable characteristics.
With this background, an object of this invention is to provide improved semiconductor pressure sensors and associated methods, and in particular, for uses which require high temperature stability and high sensitivity.
Another object of the invention is to provide a high sensitivity semiconductor pressure sensor which is easier to manufacture than competitive existing sensors.
A further object of this invention is to provide a semiconductor pressure sensor, and a related method of manufacture for dielectrically isolating single crystal silicon sensors.
Other objects of the invention are evident in the description which follows.